Shear Pin (Safety Pin)

GA for Charsley99.

I had a problem with shear pins on a large paper machine winder. (500HP motor).

Final result was due to a combination of alignment, worn shear pin holes allowing backlash, and speed tuning of the drive system that got excited with the backlash. This caused impact loading and sheared the pins. (Most winders do not have shear pins, just built beefy.)

The shear pins are designed to fail, saving other components (like fuse).

Making it stronger than the designed value will compromise the machine itself.

Check whether the pins are as per spec or these are weaker than the designed.

The breakage rate of shear pins for one of the rotor has increased recently implies that in other cases it is normal as expected. That almost rules out the defect in pin.

Sorry, don't have idea about the construction of the machine, so in general, with the machines I know, I can advice to investigate what is the problem with the rotor.

Has any bearings jammed?

any problem with clearances ? bed gap? (BTW: what is the type of crusher?)

Without being certain exactly what the design of the crusher is, I have seen a similar problem in another sort of equipment when the shaft developed a very tiny bend. In particular, this occurred in a large tumbler for deburring. As others have noted, shear pins are designed as a safety measure to protect the rest of the machine from force overload. If you are repeatedly shearing them on one rotor then most likely something else is broken and is causing increased drag on that rotor, quite possibly intermittently. If the same product is being fed by all of the rotors then it is unlikely that change in mix or product is the cause. Replacing the pin with a different rated pin of higher shear force is not recommended.

I had a similar problem 20 years ago. The pin broke twice in 2 weeks, so I replaced it with a high strength steel. The high strength steel broke in less than 2 hours. Because high strength is more brittle. To correct the problem, you need a lower strength steel that is not brittle. If that makes any sense to you.

P.E.Bobimm

pin fit is important. any slop in the fit in the shaft or rotor will break pins,

this assumes pins are to spec.

you may need to redrill in a new position, or drill oversize to get a good fit.

if oversize, be sure to spec for the proper shear characteristics.

If the pin was properly engineered, it should not need to be replaced that frequently. Perhaps the media that you are crushing is not what the pin was designed for. If the material that you are crushing is harder than the pin was designed for it will break more readily. Also there may be something binding up in the bearings or the gears may be worn to the point that they are causing a drag on the rolls.

As with most posters here I'm not familiar with your exact machine but it goes without saying that if nothing else has changed (i.e. size/compositon of material being crushed, rotational speed, etc.) then the problem must be with the alignment of the rotor. You would do good to look closer at your bearings and double-check your clearances to make sure they are within spec. I know it's always easier to say what to do than to actually do it so Good Luck!!

cheack into aTexas Crusher System replacement unit

1. As stated by others dont use higher strength materials.it may cause severe damage to machine itself
2. Has the vibration or noise increased, which will indicate the alignment problem, bearing problems
3. If the machine is motor driven check the amps, if the amps increase then it is to do with the load.Amps can also increase due to failed bearings.
4. Check the backlash of gears, is the lubrication/greasing good?.
5. The hole size for pin may have increased. As suggested by others drill a bigger hole and fit a bigger pin, tight fit with same shear props.

good luck